1. Field of the Invention
The present invention relates to an optical disk player for simultaneously reading data recorded on different areas of the optical disk. Particularly, it relates to a compact disk player (CD-player) for simultaneously reading both data of a sound signal recorded on a first recording area and other digital information such as computer programs recorded on other areas of a CD-ROM disk or a CD-I disk.
2. Prior Art
Optical disk systems are widely used in many fields. Particularly, many new CD systems such as a CD-ROM system, a CD-I (CD interactive) system and so forth are used as a storage device in a computer system. In a multimedia computer system, different kinds of digital information such as character data, image data, graphic data, program data, etc., are recorded on the CD disk together with sound data. These different data are recorded in respective areas of the CD disk. In these CD systems, a conventional CD player for music use can be commonly used.
There exist two types of disk rotation methods of the optical disk system, i.e., a Constant Angular Velocity (CAV) and a Constant Linear Velocity (CLV). In the CAV method, the optical disk is rotated at a constant speed, therefore, the recording density is higher in an inner area than in an outer area in order to obtain a constant read rate. In the CLV method, the recording density is constant in all recording areas, therefore, the rotational speed of the disk motor is controlled so as to obtain a constant linear velocity regardless of a reading position, that is, the rotational speed when an inner area is being read is higher than that when an outer area is being read. The CLV method has an advantage in that more information can be recorded on a disk, but has a disadvantage in that the control operation of a disk motor becomes complex and, in a video reproducing system, a static image cannot be obtained only by a mechanical means. The CD player adopts the CLV method.
In an optical player adopting the CLV method, the rotational speed of a disk motor is controlled by a synchronization signal included in recorded data. This recorded data is read by an optical pick-up and the synchronization signal is extracted from the read signal. The accuracy of the linear velocity is required to be within 1.2 to 1.4 m/s.
In optical players, including the CD player, only one optical pick-up is provided and it is moved according to read positions. Consequently, when reading data recorded in different areas of an optical disk such as a CD-ROM disk and a CD-I disk, these data are sequentially read by moving the optical pick-up to the corresponding reading positions. However, in the multimedia system utilizing the CD-ROM system or the CD-I system, it occurs that different data are desired to be read simultaneously. For example, an amusement game system is desired in which the reproduction of high quality music sound can be continued without an interruption while other data such as character data, graphic data, image data and program data relating to this music sound data are read from the optical disk. However, in an amusement game system including a conventional CD player, the music sound is interrupted because only one pick-up reads data sequentially.
Further, a CD-ROM system used as a storage apparatus of a computer system generally has a disadvantage in that its access speed and its read rate are inadequate. Particularly, when data recorded in different areas of a CD-ROM disk are read, a total time for completing the reading operations becomes very long.